A variety of medical conditions can be treated by implanting tubular devices into natural body lumens. For example, it is commonplace to implant metallic stents into the coronary arteries of patients with heart disease following balloon angioplasty to minimize the risk that the arteries will undergo restenosis. Recently, commercial stents have included drug-eluting polymer coatings that are designed to further decrease the risk of restenosis. Other examples of conventional tubular medical implants include woven grafts and stent-grafts that are used to span vascular aneurysms, polymeric tubes and catheters that are used to bypass strictures in the ureter and urethra, and stents that are used in the peripheral vasculature, prostate, and esophagus.
Despite the evolution of metallic stents, they continue to have limitations including potentially causing thrombosis and vascular remodeling. While biostable and biodegradable polymeric stents have been proposed to address the limitations of metallic stents, their use has been limited by a number of factors. Among these is the fact that polymeric stents are generally not as strong as their metallic counterparts, and they may undergo stress relaxation if left in a crimped delivery configuration for an extended period of time, such as during shipping and storage. In addition, many conventional stent delivery systems, particularly for self-expanding stents, grasp the stent at isolated locations or otherwise place localized stresses on the stent. For polymeric stents, this presents the possibility that the polymer becomes permanently deformed or otherwise damaged at these locations.
Another problem affects both metallic and polymer stents: a stent can move laterally as it is released from the delivery system, a phenomenon termed “stent jumping,” which may result in damage to the stent or incorrect placement, which in turn may injure the patient.
The applicants have previously described, in Douk I and II, a delivery system that can be used to deliver polymeric tubular implants, such as stents, into a lumen of a patient that minimizes the risk of stent-jumping. And, because the delivery systems of Douk I and II can be loaded with tubular implants by a user or operator in-suite just prior to implantation, the risk that the implant will undergo stress relaxation during shipping and/or storage in a loaded or crimped configuration is also minimized.
Exemplary delivery systems according to Douk I and II generally include (i) an inner shaft that comprises a distal end configured for insertion into a patient, with at least a portion of the inner shaft having an outer diameter less than an inner diameter of a crimped polymeric tubular implant; (ii) an expandable member that is slidably disposed about the inner shaft and includes an open distal end with a cross-sectional dimension that is greater than the diameter of the un-crimped polymeric tubular implant, so that at least part of the polymeric tubular implant when in an unstressed configuration can be inserted into the open distal end; and (iii) a tubular outer shaft slidably disposed over the inner shaft and the expandable member. In use, delivery devices according to Douk I and II are loaded, optionally with the aid of a loading device described below, as follows: the tubular outer shaft is retracted to expose the distal end of the inner shaft, a polymeric tubular implant is positioned around the inner shaft and the expandable member is moved to encompass at least part of the polymeric tubular implant. Finally the tubular outer shaft is advanced toward the distal end to compress the expandable member, compressing and crimping the polymeric tubular implant. The expandable member is then retracted away from the implant, leaving it ready for deployment.
To deploy a polymeric tubular implant using a device of Douk I and II, the distal end of the device is inserted into a body lumen, such as a blood vessel, and positioned at a the outer shaft is retracted away from the distal end of the inner shaft to expose the polymeric tubular implant, allowing it to expand into an unstressed shape and to make contact with the inner wall of the body lumen. A device according to Douk I and II optionally includes a second expandable member that is positioned or positionable distally to the tubular implant so that, during deployment, it can be expanded to provide a barrier to migration, then retracted to permit removal of the device from the body.
The devices described in Douk I and II reduce the likelihood of damage or mis-placement of polymeric stents, but there is a constant need in the medical device field for improvements in ergonomics, usability, safety and efficacy.